Shelf



FIG. 1 is a perspective view of a shelf showing my new design;

FIG. 2 is a front elevation view thereof;

FIG. 3 is a top elevation view thereof;

FIG. 4 is a bottom elevation view thereof;

FIG. 5 is a left side elevation view thereof; and,

FIG. 6 is a right side elevation view thereof.

The broken-line disclosure in the views is understood to be for illustrative purposes only and form no part of the claimed design. 

I claim the ornamental design for a shelf, as shown. 